console.write: no unhandled rejections from a broken pipe; FileSink write counts - #43679
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Every write to a pipe that is already broken fails on the spot, with a rejected Promise of its own. console.write() kept only the last Promise a write returned, so with several arguments a script that awaited it and caught the error still died of the unhandled rejection of an earlier argument's write. It now returns a Promise over every distinct one. The comments on the two POSIX-only tests say why they are: on Windows a write to a pipe whose reader is alive is accepted whole and returns its byte count, so there is no pending Promise for them to be about.
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…d the chain The sink's write() has three results: a count, a Promise, and `true` from a sink that is finished. Anything that was not a number was treated as a Promise, so `true` would have been added to the total as 1. `$arrayPush`, `.$then` and an index loop instead of Array.prototype.push, Promise.prototype.then and the array iterator, which a script can replace, as BundlerPlugin.ts does for the same shape.
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In `@src/js/builtins/ConsoleObject.ts`:
- Line 154: Update the aggregation call in the pending sink-write flow to use
the intrinsic Promise aggregation method, replacing the mutable global
Promise.all reference with Promise.$all while preserving the existing $then
handling and returned rejection behavior.
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src/js/builtins/ConsoleObject.ts
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`Promise.all` is a property a script can replace. The Promises are chained with `.$then` instead, and every one after the first is marked handled: its reaction is attached only once the earlier ones have fulfilled, and if one of those rejects, that is the error the caller gets. The single-Promise case falls out of the same code.
The builtin called the sink's write() once per argument and had to work out, from the JS values it got back, which Promises were the same one and which were rejections of their own. Inside the sink those are still values: a failed write is an error, a backed-up write is the sink's one pending operation. JSSink::js_write_all writes every argument, flushes once and returns one result. The first failed write ends the call with that error. The counts (a chunk written before the sink backed up, or a small one buffered beside the pending operation) are credited to that operation, so its Promise resolves to the call's total. js_write's argument handling and js_flush's body are now write_value() and flush_value(), shared with it. The builtin makes the writer as before and passes its arguments on.
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…t sizes The child checks with a writer of its own that the pipe really is broken before it calls console.write, so the test cannot pass by the writes simply being queued. A short argument beside a large one is a second shape of the same failure: the short one is buffered, and the flush then threw past the Promise of the large one.
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Inline comments:
In `@src/runtime/webcore/Sink.rs`:
- Line 627: Update the result assignment in the pending write settlement logic
so it only replaces operation.result with Writable::Owned when the existing
result is not Writable::Err; preserve later write failures so
FileSink::to_result returns a rejected Promise.
In `@test/js/bun/console/console-write.test.ts`:
- Around line 149-153: Replace the parameterized test.each block for “an awaited
console.write to a broken pipe fails once” with describe.each using the same
cases, then move the assertion flow into a nested test that receives each case’s
label and args.
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src/codegen/generate-js2native.tssrc/js/builtins/BunBuiltinNames.hsrc/js/builtins/ConsoleObject.tssrc/runtime/webcore/FileSink.rssrc/runtime/webcore/Sink.rstest/js/bun/console/console-write.test.ts
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A write that fails beside a pending operation puts its error in the operation's result and returns the operation. Crediting this call's counts then overwrote that result with the byte total. The Promise still rejected, but only because the flush that follows hits the same broken pipe and stores the error again. The result is now refreshed only when it is the running total.
…ter a failed write A later argument's write can settle the sink's pending operation on the spot, when the reader has made room and the chunk goes out with what was buffered before it. The counts were then credited to a slot that was no longer pending: this call's total lost them, and the next operation started from them. The loop now checks after every write, and carries a settled operation's value on as a count. A failed write returned without flushing, so a short chunk buffered before it was left for the auto flusher, which marked the sink finished: every later console.write reported 0 bytes and no error. The failed path flushes too; later writes fail with EPIPE as they do after any other failed call.
JSSink<T> is compiled once per sink type, and turning a flush's result into a JS value or a thrown error does not depend on the type.
The POSIX streaming writer buffers a chunk below its chunk size and
reports it as written. When a later write found the buffer not empty, it
appended its chunk, wrote the whole buffer to the fd and returned that
count, so `sink.write("a")` returned 1 and the 40000 byte write after it
returned 40001. The same happened to bytes a pending write had already
been credited with.
`try_write_newly_buffered_data` now takes the length of the chunk being
written. The buffer goes out in order, so the bytes ahead of that chunk
are the earlier ones, and they are left out of the count.
dylan-conway
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Updated 7:27 PM PT - Sep 22nd, 2026
✅ @dylan-conway, your commit 4133870fb784a756a2d146b65298eb228c0cd73b passed in 🧪 To try this PR locally: bunx bun-pr 43679That installs a local version of the PR into your bun-43679 --bun |
…r its Promise With the pipe full and its reader stalled, a short console.write() is buffered and the flush cannot push the buffer out. The flush left the sink with a pending Promise and console.write() returned the byte count, so when the reader then hung up the Promise was rejected with nobody holding it: a script that awaited every console.write() still died of an unhandled EPIPE rejection. When the final flush leaves an operation pending that was not there before it, the caller gets that operation's Promise, resolving to the call's total.
A sink whose write fails from the event loop (the reader hung up, the disk filled) finishes, and a write() after that returned `true`: "done, nothing wrong". The bytes were dropped and nothing said so, and console.write() reported 0 bytes written. The sink already records the error it fails with. Settling a piped stream now reads it instead of taking it, and a finished sink's write() returns it, from the three write entry points and from the writer's own "done" result. flush() had an `unreachable!()` for an error from that result; it returns the error. start() clears the recorded error: a sink started again does not answer for its last run. Two tests pinned `true` for a write after a failure and now expect the error.
Reporting the error a sink failed with is for a sink that failed while it was open. After end() or close() the sink is finished because it was closed, and a write to it is `Done` as it always was, including when that end()'s flush failed: end() has reported that error. The test for it is unchanged again.
Reverts the two commits that made a write() to a sink that had failed return the error as a rejected Promise. A script that writes lines without awaiting them and is piped into `head -1` runs to its end and exits 0: its short writes are buffered, the flush fails from the event loop, the sink finishes, and later writes return `true`. With a rejected Promise per later write, held by nobody, that script died of an unhandled rejection. A test now holds that behaviour in place.
On Windows a write goes to the pipe at once, so after the reader has gone each one fails on the spot with a rejected Promise of its own, and the script has always died of it there (Bun 1.4.0 does).
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Beyond the inline finding, I also checked the other POSIX user of StreamingWriter: Terminal (src/runtime/api/bun/Terminal.rs:186) shares PosixStreamingWriter, so the description's "FileSink is the writer's only user" is not quite right, but Terminal::write (Terminal.rs:1502-1507) discards the per-arm Wrote/Done counts and returns input_len, so the changed try_write_newly_buffered_data result does not reach it; only the comment at Terminal.rs:1497-1501 ("can even exceed input_len when prior data drains") is now stale.
Extended reasoning...
Findings were reported inline, so this note only records what else was examined. The count-subtraction change in PosixStreamingWriter::try_write_newly_buffered_data (src/io/PipeWriter.rs:860-903) alters the WriteResult seen by every PosixStreamingWriterParent; grepping StreamingWriter< shows two POSIX parents, FileSink and Terminal (WindowsNamedPipe is Windows-only). Terminal::write maps every non-error result to input_len and parent_on_write still receives the full amt, so Terminal's behavior is unchanged; its explanatory comment about counts exceeding input_len no longer describes the writer, which is a nit rather than a defect. The PR remains under a verified inline finding plus an unposted verified finding, so no approval.
The comment in Terminal::write said a count could exceed the input when earlier data drained with it. That was the streaming writer counting the earlier bytes again, which it no longer does. Terminal returns the input length either way.
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Beyond the inline findings, I also re-traced the case where a later argument's write drains the buffer and settles the pending operation synchronously (the concern raised on an earlier push): the state check at src/runtime/webcore/Sink.rs:625 now runs after write_value on every iteration, including the last argument's, so an operation settled by the final chunk is carried as a count instead of being credited to a Used slot or returned as an already-resolved Promise. The duplicate "FileSink.rs" alias in generate-js2native.ts was also looked at and is only a naming nit, not a behavior difference.
Extended reasoning...
The inline findings (the Windows lane failure in the new filesink.test.ts case and the pre-existing unhandled-rejection ordering when a later argument fails validation after the first has been accepted as the pending operation) are posted separately and rule out approval on their own. Separately, I re-checked the synchronous-settle path from a prior round by reading try_write_newly_buffered_data (PipeWriter.rs:861-903), FileSink::on_write (FileSink.rs:364-425) and WritablePending::run (streams.rs:424-450): a full drain calls run_pending, which sets the slot to Used, zeroes consumed and drops the promise's Strong ref. In js_write_all the state check sits after write_value in the same iteration, so even when the settling write is the final argument the loop converts the snapshotted consumed into a count and clears pending before the post-loop credit and flush. The only other ruled-out candidate was the second $rust() alias for the same FileSink module in the js2native table, which is a maintainability nit rather than a bug.
…ndled rejection console.write(big, 123) throws for the argument that is not something to write, after the first one has become the sink's pending write. That write's Promise was made inside the call and the throw means the caller never gets it, so when the write later failed it was reported as an unhandled rejection that nobody could have handled. It is marked handled when the call throws. What gets written is unchanged, and an operation left pending by an earlier call keeps its Promise as it was: that one is the earlier caller's.
js_write_all asked whether the sink had a pending operation, at entry and after each write. The question is whether the outstanding Promise is the one this call holds. An operation an earlier call left pending can settle during this call and this call can start one of its own, whose Promise was then left unhandled when a later argument threw. Settling can also run the script's microtasks, where a console.write() can leave the slot pending again for an operation of its own. The three checks compare the Promise: on a throw, in the loop, and after the flush.
When this call's writes joined an operation an earlier call had left pending, and a later argument settled it on the spot, the count carried on was everything that operation had consumed, the earlier call's bytes included. It is what this call gave it. The comments in js_write_all say the one thing the code cannot.
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Nothing blocking. The comments below are optional suggestions. There is no need to push a fix for them before merging.
Additional findings (outside the current diff — GitHub can't attach inline comments there):
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🟣
src/runtime/webcore/FileSink.rs— pre-existing: a script awaitingconsole.write(big)orwriter.write(big)can be told success while up to 4 KiB of that chunk is still unsent, and an EPIPE for those bytes then reaches nobody.PosixStreamingWriter::writereports a chunk it merely buffered asWriteStatus::Drained(PipeWriter.rs:919), and FileSink.rs:397-417 only skips settling onPending, sowas_pendingresolves the pending Promise while its tail is still inoutgoing. Fix: settle the pending operation only when the writer's buffer is actually empty (e.g. gate thewas_pendingblock on!has_pending_data, or report the buffered write with a status on_write does not treat as a drain), so a short write beside a backed-up one cannot resolve it early.Extended reasoning...
Trigger: stdout is a pipe with a slow reader;
p = console.write(big)is pending, and a short write (a progress line via console.write, orBun.stdout.writer().write("x")) lands while the unsent tail ofbigis under CHUNK_SIZE (4096, PipeWriter.rs:665-669) minus the short chunk. That happens whenever the remaining bytes are within 4 KiB above the pipe's free space at the last poll drain, so a few percent of arbitrary sizes.
Step that settles it: PipeWriter.rs:910-924should_buffer(len)isoutgoing.size() + len < CHUNK_SIZE, wheresize()is the unsent tail (PipeWriter.rs:1808-1809); the chunk is appended andparent_on_write(buf.len(), WriteStatus::Drained)is called (919) with the tail still buffered. The same at PipeWriter.rs:850-854 for the Latin-1/UTF-16 path.
FileSink.rs:378has_pending_datais true, but line 397 only returns early forstatus == Pending. Line 401was_pendingis true, 412-414 setresult = Owned(consumed)(consumed = the fullbig, credited at FileSink.rs:1562-1564), and 417run_pendingresolvespwith the full count.parent_on_writealso…Verification: pre-existing — trigger: a large write is pending on a pipe with a slow reader, a poll drain leaves the unsent tail below CHUNK_SIZE (4096, /home/claude/bun/src/io/PipeWriter.rs:665-669), and a short write on the same sink lands before the next drain. Mechanism verified in the current code.
PosixStreamingWriter::write(PipeWriter.rs:910-924):should_buffer(buf.len())is `outgoing.size() +…
…ntly Each has its own child, pipe or FIFO and temp directory, and shares nothing with the others.
…kes mordant checks pass (#43688) ## What cleanup and get mordant checks green: Removing unnecessary `bun_paths::string_paths::starts_with_windows_drive_letter` and point its one caller at the generic `starts_with_windows_drive_letter_t` it wrapped. ## Why Since #43650 merged, the `mordant` job fails on every PR that runs it, with a single finding over the baseline: ``` warning: function `bun_paths::string_paths::starts_with_windows_drive_letter` is public, but nothing in the workspace uses it warning: mordant: 1 finding(s) over the baseline in bun_paths ``` Currently red for this reason: #43650 (merged), #43675, #43679, #43624. Every other open Rust PR will hit it on its next rebase. The wrapper's only caller is `src/install/dependency.rs:1458`, inside a `#[cfg(windows)]` block. The mordant job runs on `ubuntu-latest`, so from its view the function has no users and `unused_pub` is correct. #43650 turned `bun_runtime` into an ordinary library with `pub(crate)` modules, which is what let mordant see this crate's items for the first time; the finding was latent before that. ## The fix The wrapper's whole body was `starts_with_windows_drive_letter_t(s)` with `s: &[u8]`. The same file already calls the generic function directly on Windows at line 1067 with a `&[u8]`, and `bun_paths::strings` already re-exports it explicitly. The call site now does the same and the wrapper is deleted. No behaviour change: same `T = u8` instantiation, both functions were `#[inline(always)]`, and the name resolves through the same re-export the existing caller uses. ## Verification Not compiled locally: my machine has no vendored deps checkout and no clang 23, so neither `bun bd` nor `bun run rust:check-all` can run. The evidence is the pre-existing `_t` call with an identical argument type in the same file; CI's Windows build and the mordant job are the real check. 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-authored-by: Claude Fable 5.1 <noreply@anthropic.com>
…handled The native version had to reproduce what the loop of write() and then flush(true) does, case by case, and kept differing from it: which error a call with a failed write and an invalid argument throws, a thrown EPIPE turned into a rejection, a Promise returned where a count was, 0 where a finished sink gave `true`. The loop is the behaviour, so it stays, exactly as it was. What was wrong is that the sink hands console.write Promises the caller never gets, and each is an unhandled rejection when the pipe breaks: a write that fails on the spot returns a rejected one of its own, a flush that cannot finish returns one, and a throw loses the one in hand. Those are marked handled. The one an earlier call returned is left alone: a later write or flush can hand it back, and it is its caller's. Sink.rs, FileSink.rs and the js2native table are as on main again.
dylan-conway
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writeFile adds up what each write reports and truncates the file to that total, so the streaming writer counting a buffered chunk twice left the file too long, ending in NUL bytes: 50004 bytes for 50002 on Bun 1.4.2.
The sink hands its pending Promise out again, to a later write, to a flush, to the next call. Marked handled while nobody held it, it reached a caller who then let it go, and the rejection that caller was always told about was not reported. A write that fails on the spot returns a rejected Promise of its own, and the sink never hands out a settled one again, so that is the one that is safe to mark, and the one the broken pipe cases lose. A Promise still pending when a call throws, or that a flush leaves behind, is as it was: those two cases are not fixed here and not changed.
dylan-conway
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console.write keeps the last Promise a write returned. A short write beside a pending one can settle it early, and a later large argument then starts a pending write of its own: the first one's bytes were left out of the total, which showed up as a total 70000 short on macOS with a slow reader. An earlier Promise has always settled by the time a write returns a different one, since the sink has one pending write at a time, so a fulfilled one's value is read and added.
The Alpine lanes have no libc.so.6, so the Linux-only test could not read the pipe's capacity there. It takes the path from libcPathForDlopen(), as test/mkfifo.ts does.
1.4.2 took the first write's result and `+=` each later one. The merged rewrite only added numbers, so a finished sink, whose write() returns `true`, gave `true` for several arguments where the release gives 2 or 3. The loop does the release's arithmetic again; only a Promise is treated differently, which is the bug. A test holds the finished sink's values in place: [true, 2, 3, 0, 1], the same on 1.4.2.
…t when it arrives A write that fails on the spot returns a Promise of its own, already rejected when write() returns it. The sink's Promise is never that: the slot gives it up before settling it, so it is still pending whenever the sink hands it out. That is decided as each result arrives and kept in a local, so nothing has to be remembered between calls, and the sink's Promise is never marked handled whatever happens to it later. BunBuiltinNames.h is as on main again.
#44072) ### Problem - `test/js/bun/console/console-write.test.ts:134` fails on macOS with `- "caught EPIPE` / `+ "caught ENOTCONN`. - The case closes the reader while the child writes 8 MB. The macOS kernel fails the write that the close lands in with `ENOTCONN`, not `EPIPE`. - #43649 added the case and expects `EPIPE` only. Builds 121009 and 120123 were red: each attempt failed with this or with the unhandled rejection that #43679 fixes. ### Fix - On macOS the case accepts `caught EPIPE` or `caught ENOTCONN`. Other platforms accept `caught EPIPE` only. - The case still requires a rejected promise, no other stderr output, and exit code 0. - Verified on a CI Mac (macOS 26.6.1, M2), `main` canary, 150 runs of the file. `caught ENOTCONN` fails 7 runs of the old file and 0 runs of the new file. - `bun bd test test/js/bun/console/console-write.test.ts` passes on Linux. ### Background - `Bun.spawn` gives a child with `stdout: "pipe"` one end of an AF_UNIX socketpair. - XNU `sosend()` tests for `EPIPE`, then unlocks the socket to copy the bytes. `uipc_send()` then tests "connected" first and returns `ENOTCONN`. Each later write returns `EPIPE`. - Considered a retry in `try_write_with_write_fn` (`src/io/PipeWriter.rs:84`) so that the writer reports `EPIPE`. #40935 decided that Bun passes the kernel errno through, as Node does. Node gave `ENOTCONN` in 65 of 150 runs of this scenario. - The unhandled rejection still fails 67 of those 150 runs. With #43679 and this PR the file passes 100 of 100 runs. <details><summary>Notes</summary> **This PR changes one test.** No file under `src/` changes. **Kernel path** (xnu-12377, `bsd/kern`): - `sosendcheck()` (`uipc_socket.c`) tests `SS_CANTSENDMORE` first and returns `EPIPE`. - `sosend()` calls `socket_unlock()` before the `uiomove` copy and `socket_lock()` after it. It calls `pru_send` with no second state test. - `uipc_send()` (`uipc_usrreq.c`, `SOCK_STREAM` branch) tests `SS_ISCONNECTED` first (`ENOTCONN`) and `SS_CANTSENDMORE` second (`EPIPE`). - `soisdisconnected()` (`uipc_socket2.c`) clears `SS_ISCONNECTED` and sets `SS_CANTSENDMORE` in one step. - `write(2)` on a socket takes the same path (`soo_write()` calls `sosend()`). **C probe, no Bun and no Node.** An 8 MB write on an AF_UNIX socketpair with 512 KB buffers. The peer reads one chunk and closes. 500 runs each. | host | macOS | non-blocking `send()` | blocking `write()` | | --- | --- | --- | --- | | M2 mini | 26.6.1 arm64 | `ENOTCONN` 141 | `ENOTCONN` 396 | | M2 Ultra | 15.7.9 arm64 | `ENOTCONN` 442 | `ENOTCONN` 392 | | Intel i7 | 14.8.9 x64 | `ENOTCONN` 1 | `ENOTCONN` 287 | | Linux x64 | | `ENOTCONN` 0 of 300 | `ENOTCONN` 0 of 200 | All other runs gave `EPIPE`. So the errno is not specific to macOS 26 or to one machine. With the default socket buffer size the M2 mini gave `EPIPE` in 500 of 500 runs. One more write directly after the `ENOTCONN` returned `EPIPE` in 1659 of 1659 runs. A socket that was never connected returns `ENOTCONN` on each write. **The scenario of the test**, on the M2 mini (macOS 26.6.1), Bun `1.4.3-canary.1+37da174d5`, Node v26.3.0: | parent | child | `EPIPE` | `ENOTCONN` | | --- | --- | --- | --- | | bun | bun, `await console.write(big)` | 63 | 137 | | bun | bun, `process.stdout.write(big, cb)` | 66 | 84 | | bun | node, `process.stdout.write(big, cb)` | 145 | 55 | | node | node, `process.stdout.write(big, cb)` | 85 | 65 | On macOS 14.8.9 x64, node parent and node child: `ENOTCONN` in 18 of 200 runs. **Runs of the test file** on the M2 mini: | binary | test file | runs | failed | failures | | --- | --- | --- | --- | --- | | `main` canary | `main` | 150 | 76 | 7 `caught ENOTCONN` (one argument), 69 unhandled rejection (several arguments) | | `main` canary | this PR | 150 | 67 | 67 unhandled rejection (several arguments) | | #43679 (4133870) | #43679 | 100 | 3 | 3 `caught ENOTCONN` (one argument) | | #43679 (4133870) | #43679 merged with this PR | 100 | 0 | | The test on `main` stays flaky on macOS until #43679 merges. **The decision in #40935.** An earlier revision of #40935 folded `ENOTCONN` into `EPIPE` in `write_to_socket`. The merged commit (118fdd2) dropped the fold: "The kernel errno is passed through unchanged." Node accepts both codes on macOS in its own test (`test/js/node/test/parallel/test-cluster-concurrent-disconnect.js:27-33`). At that time the race was not reproduced (1100 runs, all `EPIPE`). The probes above reproduce it. This PR keeps the decision. **`process.platform` and not `isMacOS`.** #43679 changes the `harness` import line of this file. The test reads `process.platform` so that the two PRs merge in either order with no conflict (checked with `git merge-tree`). **The same errno in other tests.** In the annotations of the last 60 finished builds, `ENOTCONN` appears in the output of three test files: this one, `test/js/bun/util/filesink.test.ts` (#43794 removes the race there) and `test/js/node/process/process-stdin.test.ts` (#42260 ignores the code on macOS). </details> <!-- robobun:evidence:begin --> --- **no test proof** · iteration 0 · platform-specific test(s) that do not run on this machine, deferring to CI, which covers all platforms: test/js/bun/console/console-write.test.ts <!-- robobun:evidence:end -->
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What does this PR do?
Two bug fixes. Nothing else about
console.writeorFileSinkdiffers from Bun 1.4.2; the last section says how that was checked.The first one is what makes
console-write.test.tsflaky onmain(an awaited console.write rejects with EPIPE when the reader has hung up (several arguments):caught EPIPE, then an uncaughtEPIPE). When the reader goes away while the large argument is still being written, that write fails on the spot,"tail"is buffered, the flush throws, and the first write's rejected Promise is lost. The test's scenario, 200 runs at 8 at a time on a debug build: 5 failures withmain'sconsole.write, 0 in 600 with this one.1.
console.writeto a broken pipe lost rejected Promises, and each was an unhandled rejectionconsole.writeis a loop ofwriter.write(argument)and thenwriter.flush(true), and that is unchanged. A write to a pipe that is already broken fails on the spot and returns a rejected Promise of its own. The caller gets the last one; any other was lost, and nobody could have handled its rejection, so a script that awaitedconsole.writeinsidetry/catchstill died of it:await console.write(big, big).flush(true)throws when a short argument is still buffered, which lost the Promise of a large argument beside it:await console.write(big, "\n"), in either order.console.write(big, 123).Such a Promise is marked handled (
$pokePromiseAsHandled). It is told apart as it arrives: a write that fails on the spot returns a Promise of its own, already rejected whenwrite()returns it, while the sink's one shared Promise is still pending whenever the sink hands it out (the slot gives it up before settling it). The sink's Promise is never marked, whatever happens to it later, because the sink hands it out again, to a later write, a flush or the next call, and marking it would silence a rejection a fire-and-forget caller has always been told about. Nothing is remembered between calls.What the caller gets is what it got before: the same return values, the same thrown errors, the same bytes written.
That includes what is not a Promise. 1.4.2 took the first write's result and
+=each later one; the merged #43649 only added numbers, so a finished sink, whosewrite()returnstrue, gavetruefor several arguments where the release gives2or3. The loop does the release's arithmetic again, and a test holds a finished sink's values in place ([true, 2, 3, 0, 1], the same on 1.4.2).One wrong value in the merged #43649 is corrected with it.
console.writekeeps the last Promise a write returned; a short write beside a pending one can settle it early, and a later large argument then starts a pending write of its own, so the first one's bytes were left out of the total (console.write(a, "s", b)resolving to1 + b; found as a total 70000 short on macOS with a slow reader). An earlier Promise has always settled by the time a write returns a different one, so a fulfilled one's value is read and added.2.
FileSink: a write that flushes earlier chunks counted them againThe POSIX streaming writer buffers a chunk below its chunk size and reports it as written. A later write that found the buffer not empty appended its chunk, wrote the whole buffer to the fd, and returned that count:
try_write_newly_buffered_datanow takes the length of the chunk being written: the buffer goes out in order, so the bytes ahead of that chunk are the earlier ones, and they are left out of the count. Bun 1.4.2 has the bug on Linux and macOS; Windows has its own writer and is correct.Two things add these counts up, and both were wrong:
fs.promises.writeFile(path, asyncIterable)truncates the file to the total, so a short chunk followed by a long one left the file too long, ending in NUL bytes: 50004 bytes for 50002 on Bun 1.4.2, where Node writes 50002.await console.write(a, b)could resolve to more than it wrote.The writer has two users on POSIX,
FileSinkandBun.Terminal.Terminal::writeignores these counts and returns the input's length, so it is unaffected; its comment about a count exceeding the input described this same over-count and is updated.Not changed
console.write(big, 123)whilebigis backed up and has not failed. Both behave exactly as on Bun 1.4.2.true. A script that writes lines without awaiting them and is piped intohead -1relies on it: it runs to its end and exits 0. A new test holds that in place (POSIX; on Windows each write fails on the spot and that script has always died).How did you verify your code works?
ERR_INVALID_ARG_TYPEon both), a failed write followed by a valid one (EPIPEthrown on both), the return value once the sink has finished, a short write to a full pipe whose reader then leaves (5, an unhandled rejection, thentruefor a later call, on both), a fire-and-forget call after a short write or after a call that threw (its rejection is reported on both), a later call handing back an earlier call's Promise, anotherthis, stdout as a terminal, and five argument shapes written to an already broken pipe. The only differences are theunhandledRejectionlines of the three cases above, and Typecheck the built-in modules (src/js) in CI #43649's"[object Promise][object Promise]".1048577for 1056869 bytes before that fix.console-write.test.tscases and the newwriteFiletest fail on Bun 1.4.2 and pass here; the tests that were already in those files pass on both.console-write.test.ts(11),filesink.test.ts(71),fs-promises-writeFile-async-iterator.test.ts(3) andbun-write.test.js(85) pass.FileSinkwrites above, as a standalone script, give[1, 40001, 7, 40007]on Bun 1.4.2 on Linux and macOS and[1, 40000, 7, 40000]on Windows; here they give the latter (filesink.test.tsimportsbun:internal-for-testing, so it cannot itself run on a release build). The same counts throughBun.file().writer(),Bun.spawnstdin and the Latin-1 and UTF-16 paths were checked the same way.await console.write(40 KiB, "ab")30000 times piped tocat: 0 wrong totals.head -1exits 0. All correct.tsc -p src/jsandbun lintpass.